An enigmatic brainstem posterior fossa ganglioglioma in an adult.

Ganglioglioma is a rare central nervous system neoplasm representing 0.4% to 1.7% of all brain tumors and most frequently occurs in the pediatric population with an incidence of 7.6%. These tumors are usually slow-growing and well-circumscribed solid or cystic lesions. Gangliogliomatosis infrequently occurs in the frontal lobe, pineal gland, basal ganglia, hypothalamus, and optic chiasm, with very few reports of brainstem ganglioglioma. We report a case of a 35-year-old female who initially presented with headache, vertigo, ataxia, saccadic dysfunction, dysarthria, and dysmetria for several years due to an unknown etiology. Her brain imaging showed multiple lesions in the pons and the cerebellum with cystic changes and size reduction and enlargement over the next few years while her neurological symptoms continued to worsen. The patient received courses of steroid treatment that improved her neurological symptoms, suggesting an inflammatory component of her disease. Extensive workup for an inflammatory or infectious etiology was unfruitful and two brain biopsies were inconclusive. A third biopsy showed atypical glial nuclei, binucleated cells, and Rosenthal fibers and the presence of BRAF V600E mutation was detected. The diagnosis of gangliogliomatosis was consequently established. This case illustrates that gangliogliomatosis may present with the waxing-and-waning neurological signs and symptoms. It can masquerade inflammatory processes in the central nervous system on brain imaging and deserves careful consideration in the diagnosis of patients with an indolent course of neurological deterioration.